Process of making indigo coloring-matter.



UNITED STATES PATENT OFFICE.

HENRY STALAY ARTHUR HOLT, OF LUDWIGSHAFEN-ON-THE-RHINE, XJrERMANY, ASSIGN'OR TO BADISOHE ANILIN & SODA FABRIK, OF

LUDVVIG-SHAFEN-ON-THE-RHINE, GERMANY, A CORPORATION.

PROCESS OF MAKING INDIGO COLORING-MATTER.

Specification of Letters Patent.

.r'atented May 15, 1906.

Application filed December 4, 1905. Serial No. 290,278.

To all whom it may concern.-

Be it known that I, HENRY STALAY An- THUR HOLT, doctor of philosophy and chemist, asubject of the King of England, residing at Ludwigshafen-on-the-Rhine, in the Kingdom of Bavaria, German Empire, have in vented new and useful Im rovements in the Production of Indigo Co oring-Matters, of which the following is a specification.

When air is passed through an alkaline solution of a leuco indigo compound, the indigo hasa tendency to separate out in a finelycrystalline condition, which is less suitable for use, especially for dyeing and printing, than is a very'finelydivided condition. I have discovered that indigo can be obtained in the desirable very finely-divided conditidn, and therefore in a condition very advantageousfor use for all purposes, by causing the oxidation to take lace in the presence of a soap, which may e done by adding to the alkaline solution of the leuco indigo compound before'passing air through it a saturated l'atty acid or an unsaturated fatty acid or a resin acid or an alkali salt of an of such acids. 1 find. soft soap particulary useful for the purposes of my invention. Instead of air other suitable oxidizing agent may be employed in carrying, out my invention.

The following are examples of how my invention can be erformed using air as the 0xidizing agent; ut m invention is not confined to these examp es. The parts are by weight. 1

Example 1:'D issolve one hundred (100) parts of indoxylic acid in two thousand five hundred (2,500) parts of waterto which the necessary quantit of caustic soda. has been added. Then ad ten (1 0) parts of soft soap (or other alkali salt of a fatty acid or of a 40 strong current of air through the solution,

the indigo being precipitated in a very fine condition. The sus ension is treated with common salt before it is filtered.

Now What I claim is 1. The process for the production of finely- 5 5 divided indigo by oxidizing an alkali solution of a leuco indigo compound in the presence of a soap.

2. The process for the production of finelydivided indigo by oxidizing an alkali solution of a leuco indigo compound in the presence of soft soap. I

In testimony whereof -I have hereunto set my hand in the presence of two subscribing witnesses.

HENRY srALAr ARTHUR m.

Witnesses:

J. Auto. LLOYD, Jos. H. Laure. 

